1. Field of the Invention
This invention relates to modified thermoplastic, segmented copolyester elastomers having improved adhesion properties, to blends of such modified elastomers with one or more compatible low molecular weight thermoplastic resins and to a method for preparing such blends.
2. Description of the Prior Art
Segmented copolyester elastomers and thermoplastic compositions containing such elastomers and low molecular weight thermoplastic resins are known.
In U.S. Pat. No. 3,832,314 there are disclosed thermoplastic compositions containing (A) 1 to 99 percent by weight of thermoplastic segmented copolyester elastomer consisting essentially of a multiplicity of recurring short chain ester units and long chain ester units joined through ester linkages, said short chain ester units amounting to 15 to 75 percent by weight of said copolyester and being of the formula ##STR1## and said long chain ester units amounting to 25 to 85 percent by weight of said copolyester and being of the formula ##STR2## wherein R is the divalent aromatic radical remaining after removal of the carboxyl groups from aromatic dicarboxylic acid having a molecular weight of less than 350, D is the divalent radical remaining after removal of the hydroxyl groups from organic diol having a molecular weight of less than 250, and G is the divalent radical remaining after removal of the terminal hydroxyl groups from long chain glycol having an average molecular weight of 350 to 6000, said copolyester having a melt index of less than 150 and a melting point of at least 125.degree. C. (DTA), and (B) 1 to 99 percent by weight of low molecular weight thermoplastic resin which forms compatible mixtures with the segmented copolyester, is thermally stable at 150.degree. C., and has a melt viscosity of less than 10,000 centipoises at 200.degree. C. Belgain Pat. No. 811,307 teaches soft thermoplastic segmented copolyester elastomer consisting essentially of a multiplicity of recurring short chain ester units and long chain ester units joined through ester linkages, said short chain ester units amounting to 15 to 50 percent by weight of said copolyester and being of the formula ##STR3## and said long chain ester units amounting to 50 to 85 percent by weight of said copolyester and being of the formula ##STR4## wherein R is the divalent aromatic radical remaining after removal of the carboxyl groups from aromatic dicarboxylic acid having a molecular weight of less than 350, said aromatic dicarboxylic acid being 55 to 95 percent by weight terephthalic acid, D is the divalent radical remaining after removel of the hydroxyl groups from butanediol, and G is the divalent radical remaining after removal of the terminal hydroxyl groups from polytetramethylene ether glycol having an average molecular weight of 1500 to 3500, said copolyester having a melt index of less than 30 and a melting point of 90.degree. to 160.degree. C. (TMA).
The compositions of U.S. Pat. No. 3,832,314 have good bond strength as hot melt adhesives and the compositions of Belgian Pat. No. 811,307 are particularly useful as pressure sensitive adhesives. In order to provide good adhesive properties, the viscosity of the adhesive blend must be maintained at a relatively constant level. It has been found that at elevated temperatures, particularly in the range of 170.degree. to 200.degree. C., over a period of several hours the aforementioned adhesive compositions lose viscosity and hence their bonding properties are reduced.
In copending application Ser. No. 370,543, filed June 15, 1973, now abandoned, Eastman teaches that the aforementioned segmented copolyester elastomers can contain a stabilizer mixture, 1.75 to 15.0 percent by weight, based on the weight of elastomer, comprising (a) 0.25 to 2.5 percent by weight of a substantially linear polycarbodiimide having an average of at least two carbodiimide groups per molecule, and at least one compound of (b) 0.5 to 2.5 percent by weight of a hindered phenol, nitrogen-containing hindered phenol or secondary aromatic amine, (c) 0.5 to 5.0 percent by weight of phosphorous acid esters and (d) 0.5 to 5.0 percent by weight of an amino acrylate, a homopolymer thereof, or a random copolymer of ethylene and 20 to 40 percent by weight of amino acrylate compound, each of compounds (b), (c) and (d) being compatible with each other and with (a). Such stabilized elastomer compositions do not suffer appreciable loss in viscosity and have good pot life when heated to 170.degree. to 200.degree. C. for extended periods of time within the period of 12 to 24 hours.
Caldwell U.S. Pat. No. 3,459,584 teaches that tetracarboxylic acid dianhydrides, preferably pyromellitic acid dianhydride, can be reacted with certain low molecular weight hydroxyl-terminated polyesters to provide a prime coating composition. The polyesters are reacted with stoichiometric amounts of acid dianhydride. The polyester-dianhydride adducts contain about 1.2 to 15 weight percent free carboxyl groups and have a molecular weight of 400 to 8000. A related Caldwell U.S. Pat. No. 3,484,339 teaches that the reaction product of the tetracarboxylic acid dianhydride and low molecular weight polyester can be blended with particular polymers to provide, as disclosed, compositions with an improved degree of adhesion.